Fig. 3: Dynamic phase structure and cell parameter evolution.

Initial contour maps, charge-discharge curves of in situ XRD and corresponding lattice parameter changes of (a) Na0.55 and (b) Na1. c, d In situ XRD of Na.55 and Na1 at 1 C (120 mA g−1) rate. e, f In situ XRD of Na.55 and Na1 for two cycles at 5 C rate. After the first cycle, the O3 phase of Na1 disappears. g, h XRD refinement of Na0.55 and Na1 after 3 cycles at 5 C (600 mA g−1).